This invention relates to a device which enables the user to replace sealing elements of a shaft seal used for a pump or the like without the danger of the fluid being pumped leaking to the atmosphere.
When a pump is shut down for repacking or repairs of the shaft seal, it is necessary to provide auxiliary sealing means around the shaft so when the packing is removed, fluid is not released to the atmosphere. Prior art devices are available for this purpose. For example, in U.S. Pat. No. 1,028,758 issued to Mason and Hammond, there is described a stuffing box for reciprocating shafts in oil wells. The stuffing box includes packing rings which can be brought into engagement against the shaft. Davey in U.S. Pat. No. 2,853,321 describes a stuffing box incorporating means for effecting and maintaining a fluid-type seal during replacement of packing elements in the stuffing box. The means includes a tubular stuffing box concentric with a pump shaft, and a sleeve axially shiftably disposed over the shaft within the stuffing box. By axially shifting the sleeve relative to the stuffing box, it is possible to selectively establish and disestablish an axial fluid seal between the sleeve and a flange of the stuffing box.
Although both of these prior art arrangements can be effective for maintaining a fluid tight seal during replacement of packing elements around a shaft, there are many problem applications for which they are unsuitable. One such application is a pump for geothermal wells. Pumps for geothermal applications are usually rotary pumps, having a shaft extending from above ground to depths of 500 to 1500 feet. The hot water in geothermal wells is corrosive, can be under high pressure, contains solid impurities, and by thermal expansion can cause the shaft to increase in length relative to the column pipe by as much as four inches. Because of these unique problems associated with applications such as geothermal wells, conventional devices for replacement of packing elements, including those of Mason et al and Davey, are unsatisfactory.
In particular, the device of Mason et al is unsatisfactory because the pressure of the water in the well acts to press the compression packing ring against the shaft during operation. This is not a problem for some applications with only low pressure at the stuffing box such as for reciprocating shafts in oil wells, but it is a serious problem for rotary shafts in geothermal water wells. The Mason et al device is particularly unsatisfactory where a portion of the fluid being pumped is permitted to flow in the clearance between the shaft and a seal ring to cool and lubricate the shaft seal. If the device of Mason et al were used in such an application, the compression packing ring could block the flow of the fluid, resulting in rapid wear of the shaft.
The device of Davey does not work in geothermal applications because of the difference between the thermal expansion of the shaft and that of the column pipe. To accommodate that difference in linear thermal expansion, four inches of clearance are provided in the pump. Therefore, it would be necessary to move the Davey sleeve at least four inches to obtain an axial seal. Such a great amount of axial movement is impractical. This is particularly true because of the hostile nature of geothermal brines which within a very short time can deposit so much scale and so corrode the sleeve and the shaft, that axial movement is impossible.
In view of these problems, there is a need for a reliable and simple stuffing box assembly for forming a static seal around a moveable shaft, and particularly a rotating shaft used in geothermal wells.